[tip:sched/core] sched/fair: Make it possible to account fair load avg consistently

tip-bot for Byungchul Park
2015-12-04T11:55:29Z

Commit-ID: ad936d8658fd348338cb7d42c577dac77892b074
Gitweb: http://git.kernel.org/tip/ad936d8658fd348338cb7d42c577dac77892b074
Author: Byungchul Park <byungchul.park@lge.com>
AuthorDate: Sat, 24 Oct 2015 01:16:19 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 4 Dec 2015 10:34:42 +0100

sched/fair: Make it possible to account fair load avg consistently

The current code accounts for the time a task was absent from the fair
class (per ATTACH_AGE_LOAD). However it does not work correctly when a
task got migrated or moved to another cgroup while outside of the fair
class.

This patch tries to address that by aging on migration. We locklessly
read the 'last_update_time' stamp from both the old and new cfs_rq,
ages the load upto the old time, and sets it to the new time.

These timestamps should in general not be more than 1 tick apart from
one another, so there is a definite bound on things.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
[ Changelog, a few edits and !SMP build fix ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1445616981-29904-2-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 4 ++++
kernel/sched/fair.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched/sched.h | 11 ++++++++++-
3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8969a9a..32d83e4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2120,6 +2120,10 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
p->se.vruntime = 0;
INIT_LIST_HEAD(&p->se.group_node);

+#ifdef CONFIG_FAIR_GROUP_SCHED
+ p->se.cfs_rq = NULL;
+#endif
+
#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ff8ec86..efd664c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2715,6 +2715,52 @@ static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
}
}

+/*
+ * Called within set_task_rq() right before setting a task's cpu. The
+ * caller only guarantees p->pi_lock is held; no other assumptions,
+ * including the state of rq->lock, should be made.
+ */
+void set_task_rq_fair(struct sched_entity *se,
+ struct cfs_rq *prev, struct cfs_rq *next)
+{
+ if (!sched_feat(ATTACH_AGE_LOAD))
+ return;
+
+ /*
+ * We are supposed to update the task to "current" time, then its up to
+ * date and ready to go to new CPU/cfs_rq. But we have difficulty in
+ * getting what current time is, so simply throw away the out-of-date
+ * time. This will result in the wakee task is less decayed, but giving
+ * the wakee more load sounds not bad.
+ */
+ if (se->avg.last_update_time && prev) {
+ u64 p_last_update_time;
+ u64 n_last_update_time;
+
+#ifndef CONFIG_64BIT
+ u64 p_last_update_time_copy;
+ u64 n_last_update_time_copy;
+
+ do {
+ p_last_update_time_copy = prev->load_last_update_time_copy;
+ n_last_update_time_copy = next->load_last_update_time_copy;
+
+ smp_rmb();
+
+ p_last_update_time = prev->avg.last_update_time;
+ n_last_update_time = next->avg.last_update_time;
+
+ } while (p_last_update_time != p_last_update_time_copy ||
+ n_last_update_time != n_last_update_time_copy);
+#else
+ p_last_update_time = prev->avg.last_update_time;
+ n_last_update_time = next->avg.last_update_time;
+#endif
+ __update_load_avg(p_last_update_time, cpu_of(rq_of(prev)),
+ &se->avg, 0, 0, NULL);
+ se->avg.last_update_time = n_last_update_time;
+ }
+}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}
#endif /* CONFIG_FAIR_GROUP_SCHED */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index cdae23d..9a029fa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -335,7 +335,15 @@ extern void sched_move_task(struct task_struct *tsk);

#ifdef CONFIG_FAIR_GROUP_SCHED
extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
-#endif
+
+#ifdef CONFIG_SMP
+extern void set_task_rq_fair(struct sched_entity *se,
+ struct cfs_rq *prev, struct cfs_rq *next);
+#else /* !CONFIG_SMP */
+static inline void set_task_rq_fair(struct sched_entity *se,
+ struct cfs_rq *prev, struct cfs_rq *next) { }
+#endif /* CONFIG_SMP */
+#endif /* CONFIG_FAIR_GROUP_SCHED */

#else /* CONFIG_CGROUP_SCHED */

@@ -933,6 +941,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
#endif

#ifdef CONFIG_FAIR_GROUP_SCHED
+ set_task_rq_fair(&p->se, p->se.cfs_rq, tg->cfs_rq[cpu]);
p->se.cfs_rq = tg->cfs_rq[cpu];
p->se.parent = tg->se[cpu];
#endif